Coaxial t hybrid



July 26, 1960 v. J. ALBANESE COAXIAL T HYBRID 3 Sheets-Sheet 1 Filed Jan. 7', 1958 mm M NA 2 E 5 w W 7 1 M A J y K V July 26, 1960 v. J. ALBANESE COAXIAL T HYBRID 3 Sheets-Sheet 2 Filed Jan. 7, 1958 7 y 1950 v. J. ALBANEs 2,946,965

COAXIAL T HYBRID Filed Jan. 7, 1958 3 Sheets-Sheet 3 INVENTOR. (#6702 I AZEAA/ESE A 7 7 OEIVE Y6 a COAXIAL T HYBRID Victor J. Albanese, Valley Stream, N.Y.,. assignor to Bogart Manufacturing Corporation, Brooklyn, N.Y., a corporation of New York Filed 'Jan. '7, 1958, Ser. No. 707,515

20 Claims. (Cl. 333-11) This invention relates to mixers, dividers and the like,

in the microwave frequency range, and more particularly to a coaxial T hybrid with series-shunt feed. It' has already been suggested to employ a hybrid ring for desired coupling and isolation between a number of lines, In my copending application Serial No. 682,175 entitled Coaxial Hybrid Ring filed September 5, 1957, I disclose a hybrid ring, and in mycopending' application Serial No. 686,209 entitled Coaxial Hybrid with Series- Shunt Feed, filed September 25, 1957, I disclose what may betermed a bar hybrid, both of which are coaxial and suitable for use in the microwave frequency range, with simple direct coupling to standard coaxial lines. Both the ring and the bar hybrids referred to may be used for example in ECM receiver mixers, power dividers, and in guided missile and radar applications.

The primary object of the present invention is to generally improve coaxial hybrids. A more particular object is to provide such a hybrid which need not be-in ring form nor in bar form. Still another object is to provide such a hybrid which is compact. Still another object is to provide. a hybrid characterized by wide frequency tolerance, while maintaining the desired isolation between opposed lines, and the desired efficiency and low voltage standing wave ratio (VSWR) between coupled lines;

To accomplish the foregoing general objects, and other more specific. objects which will hereinafter appear, my

invention resides in the coaxial hybrid and the elements thereof, and their relation one to another, as are hereinafter more particularly described in the following specification. The specification is accompanied by drawings in which:

' Fig. 1 is a partially sectioned elevation showing a :coaxial hybrid embodying features of my invention;

Fig. 2 is a bottom plan view with one of the two body members removed;

Fig. 3 is an elevation of the inner conductor assembly; Fig. 4 is a fragmentary elevation drawn to enlarged scale and looking in the direction of the arrows 44 of Fig. 3;

Fig. 5 is a horizontal section through the inner conductor assembly taken approximately in the plane of the a line 5--5 of Fig. 3;'

Fig. 5A is a view like part of Fig. 5 but showing a modification; Fig. 6 is a fragmentary section drawn to enlarged scale and taken in the same plane as the upper portion of Fig. 1;

Fig. 7 is a bottom view of the intersection of the inner conductor assembly drawn to enlarged scale;

Fig. 8 is a bottom view similar to Fig. 2. but showing a modification; and

Fig. 9 is a view like Fig. 4 but showing a modification.

Referring to the drawing, and more particularly to Figs. land 2, the coaxial hybrid comprises a first T made up of arms 1, 2 and 3, here shown with the stem of P a t tent ed July 26, 196p "ice 2 seen that the inner'conductor12 of. arm 2, and the inner conductor '13 of arm 3, are solid. These inner conductors are separated by a gap 16 which is disposed at an angle of forty-five degrees to arms 2, 3 and '4. Referring next to Fig. 2, arm 2 has anouter conductor 22 around inner conductor 12, and arm 3 has an outer conductor 23 around inner conductor 13. 7

Referring to Fig. 6, arm 1 has a solid inner conductor 11, which is surrounded by an outer conductor 21. Figs. 3 and 4, it will be seen thatthe lower portion of inner conductor 11 is longitudinally bifurcated at 26. This forms a parallel plate transformer having approximately one quarter wave length. The furcations of conductor ll are disposed astride the gap 16 (Fig. 2) previously referred to, with one branch connected to inner conductor 12, and the other connected to inner conductor 13. Inpreferred form, the slot through conductor 11 is disposed at the same forty-five degree angle as the gap 16. The faces of the slot are plane and parallel, and are flush with the faces of the gap 16.

Arm. 4 (Fig. 2) has an inner conductor 14 and an outer conductor 24. I conductor 14 is hollow rather than solid, and referring to Fig. 5 of the drawing, hollow inner conductor 14 has a thin center conductor 28 extending in coaxial relation therewith, and the thin center conductor extends beyond the gap 1 6 as indicated at 30. It will be noted that the hollow inner conductor 14 is connected directly to the solid inner conductor 13 of arm 3. It is also surrounded by a shorting means or plug 32 at a distance of about a quarter wave from the gap 16, and reverting to Fig. 2, the shorting means 32 is disposed between the inner conductor 14 and the outer conductor 24, in order to constitute a 'balun for arm 4. V

A dummy balun is disposed opposite arm 4, and includes an inner conductor 15, and an outer conductor 25, with a shorting plug 34 therebetween, at a distance approximately one quarter wave length from the gap 16. The inner conductor 15 is connected to the solid inner conductor 12 of arm 2, as is better shown in Fig. 5. The inner conductor 15 is hollow, and has a thin center conductor30 passing coaxially therethrough, the conductor 30 being an extension of the thin center conductor 28 of arm 4. There is an additional means or core 36 short ing the inner conductor 15 and the center conductor 30 of the dummy, at a distance of about one-half wave from the gap 16. The result of this arrangement is that arm 1 is connected in shunt to arms 2 and 3, while arm 4 provides the desired series feed.

The situation is somewhat analogous to connecting a coaxial line to a dipole antenna. The grounded outer conductor of the coaxial .line (not shown) connected to arm 4 must be raised above ground potential, which is done by the balun 14, 24, 32. Arm 4 has a series connection, unlike arms 1, 2 and 3 which have a shunt connection, and such a combination of connections provides the desired isolation between arms 1 and 4, independently of frequency.

The quarter wave dummy 15, 25, 34 provides mechanical and electrical symmetry about the gap 16. The center conductor 30, shorted to the inner conductor 15 by means of a metal core 36, helps match impedance between the hybrid and the coaxial lines connected thereto.

All mention herein of quarter wave and half wave length is meant to be at the design or center frequency, and may be approximate, because the unit has good frequency tolerance.

The inner faces of the bifurcation 26 straddling the gap ldforms a parallel plate transmission line. In the case here shown, it has a characteristic lineimpedance of about one hundred ohms. It has approximately a quarter In this case, however, the inner locked against axial movement.

wave length, and therefore acts as a quarter wave choke. Thus, the conductors 12 and 13 on opposite sides of the gap 16 are not shorted by conductor 11, and instead they appear to. look into an open circuit rather than a short circuit. The approximate one quarter wave length of the choke is measuredfrom thecenter of the gap.

In Figs. 1 and 2, it will be seen that the outer conductors of the hybrid are preferably'and conveniently made up of two rectangular pieces of metal 40- and 42, these being secured together in face-to-face relation by a suitable number of connecting screws. Dowel pins at 44 (Fig. 2) may be used to insure accurate positioning of the pieces 40 and 42 when secured together. The screws are not shown in the drawing, but the many threaded holes for receiving the same are shown at 46 in Fig. 2. The inner face of each of the pieces 40 and 42 has channels which are semi-circular in section, so that when the two pieces are assembled they provide outer conductors which are circular in section. The blocks 40 and 42 provide the cruciform outer conductors 22, 23, 24, and 25 for arms 2, 3, 4 and the dummy respectively. The outer conductor for arm 1 passes through block 40 in perpendicular direction, and is best shown at 21 in Fig. 6.

In the hybrid here shown, the shorting plugs 32 and 34 are adjustable. For this purpose, they have threaded shanks 52 and 54 respectively. These are threadedly received in end blocks 56 and 58. The outer ends may be provided with flats 60, best shown in Figs. 1 and 2, to facilitate rotation. They also carry lock nuts 62 and 64 respectively. It will be evident that by loosening lock nuts 62 and 64, the threaded plugs may be rotated and thus advanced or retracted as desired to obtain optimum position, following which the adjustment may be locked by means of the lock nuts 62 and 64, which are tightened against the end blocks 56 and 58.

The end blocks 56 and 58 are square if viewed from the right or left of Figs. 1 and 2. They each have four holes in the four corners which receive screws mounting the same on the upper and lower blocks 40 and 42 of the body.

Appropriate fittings are secured to the'body to receive the coaxial cables leading to the hybrid. In Fig. 1, the fitting 70 is secured to the body by means of a flange 72 and four corners screws 74. The threaded end 76 of the fitting is dimensioned to receive the coupling part of a suitable and preferably a standard connector. The fittings 7 8 and 80 may be similar to fitting 70.

Fig. 6 shows how the inner conductor assembly may be positioned in the body. Specifically, the solid conductor 11 passes through an insulation bushing 82 which is disposed between the conductor 11 and the body. The bushing may be made, for example, of Teflon or polystyrene. It is held in registeringrecess'es in the body and the fitting, that is, both the body and the fitting 70 are recessed to receive the bushing 82, which is thereby The conductor is not held against axial movement, in this case, although it may be, if desired, as by means of a transverse insulation pin made typically of nylon.

Referring to Fig. of the drawing, conductor 12 passes through an insulation bushing 84, and conductor 13 passes through an insulation bushing 86. These are held in position by nylon pins 88. It will be understood that the fittings 78 and 80 (Fig. 2) for arms 2 and 3, are similar in construction to fitting 70, and that the insulation bushings 84 and 86 correspond to the insulation bushing 82 in Fig. 6. The latter has no nylon pin because the inner conductor assembly is anyway sufficiently rigidly held against movement by the assembly of arms 2, 3, 4 and the dummy, but a nylon pin may be used also in bushing 82. i

In passing, it may be mentioned that in my prior patent applications; axial movement relative to the bushing isprevented by use of. appropriate metal snap rings received in grooves in the solid inner conductors. I prefer not to use such snap rings in the present case be cause of the very high frequency here contemplated, which is in the X band. However, at lower frequencies, snap rings may be used in the present hybrid, and conversely, nylon pins may be used in the hybrids shown in my earlier patent applications, at higher frequencies.

Referring to Fig. 5, the thin center conductor 28, 30 is held in concentric relation to the hollow inner conductors 14, by a filling of insulation material. This may be polyethylene or Teflon. It may be continuous, or it may be in the form of assembled beads as shown ,inthe drawing. The beads 90 may be-supplemented by .washers 92 to obtain a desired length.

The hollow inner conductor .14, 94 (Fig. 5) of arm 4 changes in thickness. There is a transition at point 96.

part 14 is thinner and characterized by higher imvpedance, while the part 94 is thicker and characterized by The part 14, 28 with its thinner wall and thicker insulation has the necessary impedance of about seventy ohms.

The transition point 96 (Fig. 5) for a change in thickness is conveniently obtained by soldering together tubes of difierent wall thickness. They may overlap, as shown. The transition point is preferably located at a distance of about a quarter wave from the gap 16. Of course, the physical distance for a given wave length is different in insulation material, compared to what it is in air, and therefore the transition point 96 does not coincide with the location of the shorting plug 32.

It will be understood that the desired change in impedance at the transition point 96 might be made by a change in diameter of the thin center conductor 28, instead of by a change in wall thickness of the hollow inner conductor. In general, what is needed is a change in relative dimension, causing a change in impedance. In the present case, it is more convenient to use a continuous one-piece conductor of uniform dimension for the center conductor, which is quite thin, and to change the wall thickness of the hollow conductor.

In the case of arm 1, a change in impedance preferably is obtained by changing the inner conductor. This will be clear from inspection of Figs. 3, 4 and 6, in which the inner conductor is stepped in diameter at 98. This step is located about a quarter wave distance from the gap 16, and causes a change from an impedance of approximately fifty ohms in the upper portion, which receives an outside fifty ohm cable connected to the fitting 70, to an impedance of about thirty-five ohms below the step 98 where the inner conductor is enlarged. Arms 2 and 3 have an impedance of fifty ohms each, and are connected in shunt, so that arm 1 looks into an impedance of twenty-five ohms. The thirty-five ohm impedance below the step 98 helps match the fifty and twenty-five ohm impedances. The step 98 in conductor 11 is located about a quarter wave distance from the outside or top of the inner conductors 12 and 13, rather than from the center point of the gap 16, and this is higher than the slot 26.

' The fitting 100 for am 4 also receives a fifty ohm cable. Referring to Fig. 5, the inner conductor 102 of fitting'100'is larger in diameter than the thin center conduotor28. In the hybrids of my aforesaid copending applications, the necessary transition was obtained by a step in diameter of appropriate length. Any resulting capacitive shunt' react-ance was counteracted by inductive impedance. However, in the present case, the frequency is so high thatthe capacitive susceptance which would be created by an abrupt step would create a mismatch, and a high VSWR (voltage standing wave ratio). Instead, a long taper is used, as shown at 104. The insulation bushing 106 is similarly tapered. This provides a gradual transformation of the line size. The parts 28, 94 have an impedance of about fifty ohms, and the parts 100, 102 also have an impedance, of about fifty ohms, and the special tapered construction is employed therebe-tween in order to avoid the use of an abrupt step. A nylon pin may be used at 108 to hold the part 102 against axial movement, as when applying or removing a cable connector to fitting 100. A metal block 206 receives fitting 100, and houses bushing 106. The block is secured to conductor 94.

At the end of the dummy, the thin center conductor 30 is shorted to the hollow inner conductor 15 by metal core 36. This short is at a distance of about a'half wave length from the gap'16, and is an additional means to help obtain the desired impedance match with the arms of the hybrid (and the cables leading thereto). The quarter wave choke for the dummy uses air as a dielectrio, and is formed by the parts 15, 25, 34 (Fig. 2). This quarter wave chokeis for symmetry with the balun on arm 4.

There is isolation between arms 2 and 3 which isolation depends on a rather complex network theory which is not necessary to go into here, because for all, practical purposes, the present hybrid is intended to establish isolation between arms 1 and 4, regardless of the existence or nonexistence of isolation betweenarmsZ and 3, which is of relatively small importance.

Adjustable shorting plugs are of value primarily in experimental work. The present hybrid does not depend on path length for isolation between arms 1 and 4. Rather, it relies on its combination of series and shunt feed, and is therefore characterized by good frequency tolerance. The hybrid is slightly aifected by frequency tolerance in respect to the quarter wavechoke action of the balun and the dummy and the parallel plate line 26, and in respect to proper impedance match. It has a frequency tolerance of, say plus or minus twenty-five percent of the design frequency, or a tolerance of fifty percent in all, even with fixed shorting plugs.

The hybrid therefore may be simplified by the pro- Vision of fixed shorting plugs instead of adjustable shorting plugs. Such a modification is shown in Fig. 8 of the drawing. This resembles Fig. 2 in that the lower half of the rectangular body has been removed, thus exposing the upper half 110. This has a cruciform channel which is semicircular in cross section. Together with a mating cruciform channel in the lower half of the body, a cruciform hollow conductor is formed which is circular in cross section. -The inner conductors 112 and 113 are solid, and are separated by agap 116. The inner conductors 114, 115 arehollow, as previously described, and are shorted to their respective outer conductors by means of shorting plugs 132 and 134. The connections are preferably soldered, and no end plates corresponding to the square internally threaded end plates 56 and 58 (Figs. 1 and 2) are needed. In other words, the simple soldered shorting plugs 132 and 134 (Fig. 8) replace the threaded shorting plugs and their mating end plates and their lock The fittings 180 and 178 may be the same as previously described. Also the fitting 200 for arm 4 may be the same as previously described, and is similarly connected by means of its square flange 202 and four corner screws 204 to a block 206, which is secured at the free end of outer conductor 194, and within which block the tapered connection previously described in Fig. 5 is provided.

In general, except for the elimination of the adjustable shorting plugs, all of the features previously described are similarly applicable to the modified form of coaxial T hybrid shown in Fig. 8.

The inner conductors within the fittings are split at their free ends and act as the inner connection of the fittings, which otherwise may be standard. Each fitting has a generally cylindrical body 70 (Fig. 1), with a square flange 72 at its base, mounted in position by means of four corner screws 74. The upper end of the body is threaded at 76 to receive the matingly threaded coupling part of a standard coaxial cable connector. The fitting here shown receives an N type connector, but appropriate change in design may be made to receive a BNC type connector, or other types of coaxial connector.

The center conductor 28, 30 (Fig. 5) is quite slender, say 0.030 inch in diameter, which is an easily available conductor size. The gap at the interruption 16 is quite small, say 0.050 inch, but this dimension is not critical. Appropriate changes in other dimensions must be made for hybrids intended to operate at different frequency.

The diameters for the outer conductor channels and for the inner conductors are not given because the impedance depends on their relative diameter, and on the nature of the dielectric therebetween. A vast number of combinations of relative dimension are possible.

The metal used for the structure may be varied. For many purposes, brass is desirable because of its good conductivity and corrosition resistance. However, aluminum is also'preferred, particularly for airborne equipment, in orderto combine good conductivity and corrosion resistance with light weight. The insulation around the .thin center conductor may be Teflon or polyethylene.

The insulation bushings in the fittings may be Teflon or polystyrene. The hybrid may be bodily oriented in any desired position. 7

While I have shown arm 4 connected to arm 3 (Fig. 2), and the dummy connected to arm 2, it will be understood that these are interchangeable, and that arm 4 could be'connected to arm 2, with the dummy then connected to arm "3. This amounts merely to a change in the nu-- merical designation of the arms.

It;will also be understood that while simple direct fittings have been shown, it is possible to use more complex' fittings, for example, angle fittings. By using angle fittings for, arms 2 and 3, the cables leading thereto may approach in a direction generally collateral to the cable arm .1.

In Fig. 5, the change in thickness of the hollow inner conductor "14, 94 is most readily obtained by assembling two tubular parts. The part 14 is the thin walled part, and the left end of part 94 which is the thick walled part, is steppedor reduced in diameter to be received telescopically in part 14. The location of the inside or left end of part 94 determines the location of the transition point 96 where the efiective change in thickness takes place. For experimental purposes, this location may be varied by the addition of small metal washers at 95, and corresponding insulation washers at 92. -In a final design, the metal washers 95 would not be needed because the parts would be initially made of proper length.

indeed, with frequencies above say 7,000 mc.,one may dispense with the step in the thickness of the hollow inner conductor, and such a modification is shown in .Fig. 5A, which is like Fig. 5 in having the solid conto 8,000 me, whereas the uniform tube shown in Fig. SA 7 is suited for a frequency range above say 7,000 mc.

If used at similar high frequencies, slight variations in the method of obtaining impedance matching in arm -1 may be used. For example, the one-quarter wave matching transformer shown in arm 1 may be replaced by a matching device which comprises a capacitive disc in the coaxial line forming a part of arm 1, as shown in Fig. 9. The quarter wave transformer illustrated in Fig. 4 is preferred in a frequency range of from say 4,000 to 8,000 me, and the capacitive disc is preferred in a frequency range of from say 7,000 to 11,000 mc.

Referring to Fig. 9, the solid conductor '11 has no step like that shown at 98 in Fig. 4, and instead has the disc 99. This is radially slotted at 27 and diametrically opposite slot 27, in order to maintain the slot 26'. The resulting less-than-half discs are soldered in position.

In the particular case shown, used at a center frequency of 9,000 me, the inner conductors 1-1, 12 and- 13' are all 0.125 inch in diameter. The outer conductors -'-are 0.288" LD. The disc 99 is 0.032 thick and 0.230 in diameter, the slot 26' is 0.0440 wide, the slot is 0.301 long from the axis of inner conductor 12', and the bottom of the disc'is 0.144 inch from the said axis.

At low frequencies, a step transition may be used at the outer end of arm 4 instead of the taper shown in Fig. 5. Such a taper grows inconveniently long at lower frequencies, say 5,000 mc., or less. An alternative step transition is shown in my two copending applications, Serial No. 682,175 and No. 686,209 previously mentioned.

In general, the coaxial T hybrid here disclosed is useful in frequency ranges centering on 3,000 to 9,000 mc., plus or minus twenty-five percent for each center frequency. Thus, the full range might be about 2,200 to 11,000 me. At the lower end of the range, snap rings may be used.

It will be understood that the various chokes heretofore referred to as being a quarter Wave long might instead be "made three quarters or five quarters, etc. waves long. This applies to the balun on arm 4, the dummy balun, and the parallel line plate choke or bifurcation 26 on arm 1.

It is believed that the construction, method of design and method of use of my new hybrid, as Well as the advantages of the same, will be apparent from the foregoing detailed description. It will also be understood that while I have shown and described the invention in several preferred forms, changes may be made in the structures shown, without departing from the scope of the invention, as sought to be defined in the following claims.

I claim:

1. A coaxial hybrid of the series shunt type for frequencies in the microwave band, said hybrid comprising a first T made up of arms 1, 2 and 3, and a second T I made up of arms 2, 3 and 4, with arm 4 disposed transversely of arm 1, so that the second T is in a plane transverse to that of the first T, arms 2 and 3 each having a solid inner conductor and an outer conductor, with their inner conductors separated by a gap' disposed at an angle of 45 degrees to arms 2, 3 and 4, the inner conrductor of arm 1 being longitudinallyv bifurcated at its inner end to form a parallel plate transformer having approximately a quarter wave length, the furcations of the inner conductor of arm 1 being disposed astride the -gap, with one furcation connected to the inner conductor of arm 2 and the other furcation connected to the inner conductor of arm 3, arm 4 having an outer conductor and an inner conductor which is hollow and has a thin center conductor extending through the inner conductor, :said hollow and center conductors of arm 4 afiording external connection to arm 4, said inner conductor of :arm 4 being connected to arm 3,'a shorting means between the inner and outer conductor of arm 4 at a distance of about a quarter wave from the gap to form a balun for arm 4, whereby arm 1 is connected in shunt to arms 2 and 3, while arm 4 provides the desired series feed.

2. A coaxial hybrid of the series shunt type for fre- 'quencies in the microwave band, said hybrid comprising a first T made up of arms 1, 2 and 3, and a second T made up of arms 2, 3 and 4, with arm 4 disposed transversely of arm 1, so that the second T is in a plane transverse to that of'the first T, a dummy balun opposite arm 4, arms 2 and 3 each having a solid inner conductor and an outer conductor, with their inner conductors separated by a gap disposed at an angle 45 degrees to arms 2, 3 and 4, the inner conductor of arm 1 being longitudinally bifurcated at its inner end to form a parallel plate transformer having approximately a quarter wave length, the furcations of the inner conductor of arm 1 being disposed astride the gap, with one furcation connected to the inner conductor of arm 2 and the other furcation connected to the inner conductor of arm 3, arm 4 having an outer conductor and an inner conductor which is hollow and has a thin center conductor extending through the inner conductor beyond the gap, said hollow and center conductors of arm 4 affording external connection to arm 4, said inner conductor of arm 4 being connected to arm 3', a shorting means between the inner and outer conductor of arm 4 at a distance of about a quarter wave from the gap to form a balun for arm 4, an inner conductor disposed opposite arm 4 in the dummy, said inner conductor being connected to arm 2 and being hollow and having a thin center conductor which is an extension of the thin center conductor of 'arm 4, and means shorting the inner and center conductors of the said dummy at a distance of about a half wave from the gap, whereby arm 1 is connected in shunt to arms 2 and 3, while arm 4 provides the desired series feed.

3. A coaxial hybrid of the series shunt type for frequencies in the microwave band, said hybrid comprising a first T made up of arms 1, 2 and 3, and a second T made up of arms 2, 3 and 4, with arm 4 disposed perpendicular to arm 1 so that the second T is in a plane perpendicular to that of the first T, arms 2 and 3 each having a solid inner conductor and an outer conductor, with their inner conductors separated by a gap disposed at an angle of 45 degrees to arms 2, 3 and 4, the inner conductor of arm 1 being longitudinally bifurcated at its inner end to form a parallel plate transformer having approximately a quarter wave length, the furcations of the inner conductor of arm 1 being disposed astride the 7 gap, with one furcation connected to the inner conductor of arm 2 and the other furcation connected to the inner conductor of arm 3, arm 4 having an outer conductor and an inner conductor which is hollow and has a thin center conductor extending through the inner conductor beyond the gap, said hollow and center conductors of arm 4 afiording external connection to arm 4, said inner conductor of arm 4 being connected to arm 3, a shorting means between the inner and outer conductor of arm 4 at a distance of about a quarter wave from the gap to form a balun for arm 4, a dummy balun disposed opposite arm 4 and including inner and outer conductors with a shorting plug at about a quarter wave length from the gap, said inner conductor being connected to arm 2 and being hollow and having a thin center conductor which is an extension of the thin center conductor of arm 4, and means shorting the inner and center conductors of the dummy at a distance of about a half wave from the gap, whereby arm 1 is connected to shunt to arms 2 and 3, while arm 4 provides the desired series feed.

4. A coaxial hybrid as defined in claim 2, in which the inner and center conductors of arm 4 change in relative thickness, at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 4.

5. A coaxial hybrid as defined in claim 3, in which the inner and center conductors of arm 4 change in, relative thickness at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 4.

6. A coaxial hybrid as defined in claim 2, in which the inner and center conductors of arm 4 change in relative thickness at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 4, said change taking place about a quarter wave distance from the aforesaid gap.

7. A coaxial hybrid as defined in claim 3, in which the inner and center conductors of arm 4 change in relative thickness at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 4, said change taking place about a quarter wave distance from the aforesaid gap.

8. A coaxial hybrid as defined in claim 2, in which the inner and center conductors of arm 4 change in relative thickness at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance which helps the hybrid to match the impedance of four coaxial lines all of like impedance which are to be connected to arms 1, 2, 3 and 4.

9. A coaxial hybrid as defined in claim 3, in which the inner and center conductors of arm 4 change in relative thickness at a point intermediate the gap and the free end of arm 4, the change in relative thickness causing a change in impedance which helps the hybrid to match the impedance of four coaxial lines all of like impedance which are to be connected to arms 1, 2, 3 and 4.

=10. A coaxial hybrid as defined in claim 2, in which the outer and inner conductors of arm 1 are relatively changed in diameter at a point intermediate the said gap and the free end of arm 1, the change in relative diameter causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 1, and the impedance of arms 2 and 3 connected in shunt.

11. A coaxial hybrid as defined in claim 3, in which the outer and inner conductors of arm 1 are relatively changed in diameter at a point intermediate the said gap and the free end of arm 1, the change in relative diameter causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 1, and the impedance of arms 2 and 3 connected in shunt.

12. A coaxial hybrid as defined in claim 2, in which the solid inner conductor of arm 1 is stepped in diameter at a point intermediate the said gap and the free end of arm 1 to produce a relative change in diameter of said inner conductor, the change in relative diameter causing a change in impedance to help match the impedance of a coaxial line to be connected to arm 1, and the impedance of arms 2 and 3 connected in shunt.

13. A coaxial hybrid as defined in claim 3, in which the solid inner conductor of arm 1 is stepped in diameter at a point intermediate the said gap and the free end of arm 1 to produce a relative change in diameter of said inner conductor, the change in relative diameter causing a change in impedance to help match the im pedance of a coaxial line to be connected to arm 1, and the impedance of arms 2 and 3 connected in shunt.

14. A coaxial hybrid as defined in claim 2, in which two pieces of metal are secured together to form the main body of the unit, the inner diace of each of said pieces having channels which are semi-circular in section and arranged in T relation, whereby the pieces when assembled provided the outer' conductor of arms 2, 3 and 4, one or said pieces having a cylindrical passage perpendicular to its channelled face and located at the intersection of the T channels, said passage in said latter piece acting as the outer conductor for arm 1.

15. A coaxial hybrid as defined in claim 3, in which two pieces of metal are secured together to form the main body of the unit, the innner face of each of said pieces having channels which are semi-circular in section and arranged in cruciform relation, whereby the pieces when assembled provide the outer conductor of the dummy and of arms 2, 3 and 4, one of said pieces having a cylindrical passage perpendicular to its channelled face and located at the intersection of the cruciform channels, said passage in said latter piece acting as the outer conduct-or for arm 1.

16. A coaxial hybrid as defined in claim 3, in which two pieces of metal are secured together to form the main body of the unit, the inner face of each of said pieces having channels which are semi-circular in section and arranged in cruciform relation, whereby the pieces when assembled provide the outer conductor of the dummy and of arms 2, 3 and 4, one of said pieces having a cylindrical passage perpendicular to its channelled face and located at the intersection of the cruciform channels, said passage in said latter piece acting as the outer conductor for arm 1, and in which appropriate fittings are secured to the afioresaid body for receiving at least some of the coaxial lines which are to be connected to the arms of the hybrid, some of said fittings being secured to edge walls of said body astride the two pieces, and the fitting for arm '1 being secured to the outer face wall of one of the said pieces.

17. A coaxial hybrid as defined in claim 2, in which the parallel plates of the tut-cations of arm 1 are disposed at an angle of 45 coincident with the gap.

18. A coaxial hybrid as defined in claim 3, in which the parallel plates of the furcations of arm 1 are disposed at an angle of 45 coincident with the gap.

19. A coaxial hybrid of the series shunt type for frequencies in the microwave band, said hybrid comprising a first T made up of arms 1, 2 and 3', and a second T made up of arms 2, 3 and 4, with arm 4 disposed transversely of arm 1, so that the second T is in a plane transverse to that of the first T, arms 1, 2, 3 and 4 each having an inner conductor and an outer conductor, said conductors of arms 2, 3 and 4 being coaxial the adjacent ends of the inner conductors of arms 2 and 3 being separated by a gap, the inner conductor of arm 1 being longitudinally bifurcated at its inner end to form a parallel plate transformer having approximately one-quarter wave length, the furcations of said inner conductor of arm 1 being disposed astride the gap, with one sturcation connected to the inner conductor of arm 2 and the other furcation connected to the inner conductor of arm 3.

20. A coaxial hybrid of the series shunt type for frequencies in the microwave band, said hybrid comprising a first T made up or arms 1, 2 and 3, and a second T made up of arms 2, 3 and 4, with arm 4 disposed transversely or" arm 1, so that the second T is in a plane transverse to that of the first T, arms 1, 2, 3 and 4 each having an inner conductor and an outer conductor, said conductors of arms 2, 3 and 4 being coaxial the adjacent ends of the inner conductors of arms 2 and 3 being separated by -a gap disposed at an angle of 45 degrees to arms 2, 3 and 4, the inner conductor of arm 1 being longitudinally bifurcated at its inner end to form a parallel plate transformer having approximately one-quarter wave length, the turcations of said inner conductor of arm 1 being disposed astride the gap, with one furcation connected to the inner conductor of arm 3.

References Cited in the file of this patent UNITED STATES PATENTS 2,425,379 Lindenbl-ad Aug. 12, 1947 2,507,915 Lindenblad May 6, 1950 2,643,296 Hansen June 23, 1953 2,652,544 Muchmore Sept. 15, 1953 2,769,146 Alford Oct. 30, 1956 2,877,430 Bogner Nov. 10, 1959 

